An international group of researchers working in Tibet have recovered new clues about Earth's ancient climate. These clues come in the form of ice cores taken from the Guliya ice cap, which are believed to contain information about the components of the atmosphere over the last 200,000 years.

The scientists are beginning analysis of one of the three cores recovered by the expedition last summer. Lonnie G. Thompson, leader of the research team, said that this core could reveal new insights about Earth's climate through the last four ice ages.

A better understanding of these climate patterns will inform the so-called "global warming" debate.

Some scientists believe that human-produced carbon dioxide is causing Earth to warm dangerously. This view is supported by some ice core studies. However, skeptics question this opinion, arguing that we lack evidence that the warming is not simply a natural part of the planet's climate fluctuations.

Ice cores contain atmospheric "fossils"  bubbles of preserved gases and dust from different times in Earth's history. Thompson explained that "These long-term archives will let us look at the natural variability of the climate over long periods...."

Another ice core taken from Antarctica has suggested that carbon dioxide levels and temperature have increased and decreased in sync over the past 170,000 years.

However, scientists have not yet come to a conclusion regarding the main question inspired by the ice core data: Do higher carbon dioxide levels actually cause temperature increases?